Thermal processing systems are widely used in various stages of semiconductor fabrication. Basic thermal processing applications include chemical deposition, diffusion, oxidation, annealing, silicidation, nitridation, and solder re-flow processes. Vertical rapid thermal processing (RTP) systems comprise a vertically oriented processing chamber which is heated by a heat source such as a resistive heating element or a bank of high intensity light sources. An elevator structure is controlled to move a workpiece such as a wafer workpiece on a workpiece support vertically within the processing chamber. The elevator structure of prior art RTP's typically included a vertically-oriented moveable elevator shaft which extended into the processing chamber. The workpiece support was affixed to an upper end of the elevator shaft. A lower end of the elevator shaft was coupled to a vertically moveable carriage that allowed the elevator shaft to move vertically with respect to the processing chamber and, therefore, allowed the workpiece to move vertically within the processing chamber.
In some RTP systems, the heat sources create a temperature gradient within the processing chamber and temperature ramp-up and ramp-down rates of the wafer being processed are controlled by the vertical location of the workpiece within the processing chamber. Therefore, to optimize the thermal processing of semiconductor workpieces it is important to accurately control the vertical position of the workpiece within the processing chamber.
In addition to accurately controlling the vertical position of the workpiece within the processing chamber, it is also desirable to minimize vibration imparted to the workpiece via the elevator structure. Vibration may cause the workpiece to move horizontally relative to the support, thereby losing concentricity with the support structure. Lack of concentricity results in temperature non-uniformity near the workpiece perimeter.
One approach to reducing vibration in elevator structures of prior art RTP's was providing a rigid base which was affixed to a lower end of the elevator shaft. The rigid base was thought to minimize vibration that may be transmitted through the elevator shaft and imparted to the workpiece. However, since the elevator structure does have to move vertically, the base necessarily had to be affixed to the vertically movable carriage. Thus, in spite of the rigid base affixed to the lower end of the elevator shaft, vibrations from external sources could be still transmitted through the vertically movable carriage, the base, the elevator shaft, the workpiece support and, finally, to the workpiece itself.
What is needed is a system that facilitates both accurate movement and positioning of a workpiece within the RTP processing chamber and minimizes vibration transmitted to the workpiece. What is also needed is a system that isolates the workpiece support within the processing chamber from the moveable carriage outside of the processing chamber.
What is also needed is a method that facilitates both accurate movement and positioning of a workpiece within the RTP processing chamber and minimizes vibration transmitted to the workpiece. What is also needed is a method that isolates the workpiece support within the processing chamber from the moveable carriage outside of the processing chamber.